The development of improved composite materials, particularly wood-based materials, such as plywood, oriented strand board, wafer board and the like, has led to increased use of these materials in both engineering and nonengineering applications. Despite increased demand and use, manufacturers of composite materials often suffer significant quality control problems. Wood-based composite materials can vary relatively widely in strength due to the composite nature of the products and the difficulty in achieving uniform strength in the bonding used to join the components together. Additionally, variations in the feedstocks and other factors make manufacture of uniformly strong and elastic structures from composite elements difficult and costly.
In the industries producing structural-use materials, certain performance standards and performance test methods have been promulgated by various governmental and trade organizations, e.g., the U.S. Department of Commerce and the American Society of Testing and Materials (ASTM), to insure product uniformity. A manufacturer must not only meet such product standards to qualify initially for approval of its products, but must maintain ongoing quality, i.e., must conduct a quality assurance program. To assure and maintain quality, manufacturers have an ongoing sampling program to performance test product. Typically, manufacturers must ship many samples weekly from the manufacturing site, e.g., the mill, where the products are made, to remote test centers or laboratories for performance testing. The cost of transportation and testing is significant because a manufacturer may send as many as fifty panels every week to a test site. There has been very little in the way of reliable in-house testing at the manufacturer's site.
One known test for wood-based panels is to take small samples of the panels, e.g., a 1-inch.times.5-inch coupon, and submit them to a universal test machine in which the sample is stressed to breaking. While such testing is quick and can be accomplished in-house, it has proved unreliable in identifying defects and has mistakenly identified usable product as defective, in the latter case, leading to a significant waste of usable product.
Various patents have attempted to respond to some of the problems of performance testing composite materials, especially wood products. For example, U.S. Pat. No. 4,589,288 issued to Porter et al. discloses a static bending apparatus for grading wood panels. U.S. Pat. No. 4,838,085 issued to Pellerin et al. discloses methods and an apparatus for nondestructive evaluation of various mechanical properties of composite materials. Other patents that disclose methods of inspection and grading of wood products include, Canadian Patent 918286; U.S. Pat. No. 4,313,348 issued to Madsen; U.S. Pat. No. 5,237,870 issued to Fry et al.; U.S. Pat. No. 3,194,063 issued to McKean; U.S. Pat. No. 3,513,690 issued to Pellerin et al.; and U.S. Pat. No. 5,423,991 issued to Collins.
Nondestructive inspection and testing of materials of all sorts are known. For example, U.S. Pat. No. 5,127,271 issued to Sato et al. describes a method of nondestructive inspection of resinous automotive bumper beams, while U.S. Pat. No. 4,982,609 issued to Talley, III discloses a test device for vehicle roof stiffness. Others have disclosed methods of performance testing of materials based on ultrasonic or acoustic techniques. See, e.g., U.S. Pat. No. 3,504,532 issued to Muenow et al.; U.S. Pat. No. 3,512,400 issued to Lynnworth; U.S. Pat. No. 3,858,437 issued to Jarzynski et al.; U.S. Pat. No. 4,201,093 issued to Logan; U.S. Pat. No. 4,338,820 issued to Jassby et al.; U.S. Pat. No. 4,481,820 issued to Thomann; and U.S. Pat. No. 4,492,117 issued to Chubachi. U.S. Pat. No. 2,439,130 issued to Firestone discloses the use of supersonic vibrational waves for inspection of materials qualities. U.S. Pat. No. 3,888,108 issued to Brands discloses a method for impact testing of pavements. U.S. Pat. No. 4,213,349 issued to Miura discloses a method of measuring stiffness of a test piece. U.S. Pat. No. 4,147,064 discloses using stress waves for determining elastic properties of a material.
Most of the known methods for performing certain standards tests are manual methods. For example, to conduct a concentrated load test, it is known to build a frame with beams simulating joists in a building construction. The beams are spaced apart depending upon the end use and span rating of the panel to be tested. A hydraulically-actuated load is applied to the panel at a specified distance from a non-secured edge and the deflection of the panel is measured by placing a dial micrometer under the panel at a position opposite the load and reading the deflection on the micrometer scale.
Despite recognition and study of various aspects of the quality assurance problems with wood-based panels, virtually all of the known methods are manual, labor intensive procedures that can readily lead to error or operator tampering. Most only permit testing of small sample specimens rather than full size panels. Accordingly, there is a significant need for methods and apparatus for performance testing of structural elements such as wood panels to provide a reliable quality assurance program for a manufacturer, a system which is fully automatic, eliminates human error and readings, is usable in-house by the manufacturer and permits testing of full size panels.